Electroacoustic transducer



2z, wm H'. BENIOFF 2,419,197

=`ELEGTROACOUSTIC TRANSDUCER may 3, 1940 6 Sheetsheet 1 /l L I /Z n CRYSTALS MOUNTED FOR ISODIFFERENCE IN PHASE 25 FIG. 5 I l I /4 /6 2 2 2 7 f *j* 1 /2' l v INVENTOR 5/ 4 Huso BE .A. 5," l BY gym-'E I FIG'Z Agin-roam pril 22, 1947. H. BENIOFF 2,419,197'- ELECTROACOUSTIC TRANSDUCER Filed may 3, 1940 s sheets-sheet 2 if 5 L i F. a 5 J l F U 4 s 4 FIGA FIG 6 INVENTOR j HUGO BENIoF-F www? INVENFR 6 Sheets-Sheet 3 H. BENIQFF ELECTROACOUSTIC TRANSDUCER Flled May 3 1940 E947. H BENlQFF 2,419,197

ELECTROACOUSTIC TRANSDUCER Filed May 3, 1940 6 Sheets-Sheet 4 H. BENloFF M9519? ELECTROACOUSTI C TRANSDUCER Filed May 3, 1940 6 Sheets-Sheet 5 F56. i INVENTOR www April 22, 1947. H. Bz-:NloFF ELECTROACOUSTIC TRANSDUCER Filed May 3, 1940 6 Sheets-Sheet 6 INVENTOR. Huso BemoFF ATTORNEY sur Prie i 2,419,197 stscrnoscous'rrc rasnsnncsa Hugo Benini?, La. Canada, Calif., assignor. by

mesne assignments, to Submarine Signal Company, Boston, Mass., a corporation of Delaware The present invention relates to velectroacoustic transducers and particularly to such transducers for underwater use for transmitting and receiving compressional waves. Still more particularly the present invention relates to electroacoustic transducers in which the active element consists of one or more piezoelectric crystals.

The'various objects and features of the invention as well as the manner of construction andoperation will best be understood from the following description taken in connection with the accompanying drawings in which Fig. 1 is a horizontal section through one modification of the invention; Fig. 2 is a fragmentary transverse `mid-section taken along the line 2-2 of the device shown in Fig. 1; Fig. 3 is a fragmentary transverse mid-section of a modication of the arrangement shown in Fig. 2; Fig. 4 is a fragmentary horizontal section of a. further modication of the invention; Fig. 5 is a transverse fragmentary section taken along the line 5--5 in Fig. 4; Fig. 6 is a transverse section taken along the line B-t in Fig. 4; Figs. 7 and 8 show a modification of the arrangement of Figs. 1 to 3, Fig. 'l showing the right half in plan and the left half in section along the line 1--1 in Fig. 8, and Fig. 8 showing the lett half of Fig. in elevation and the right half in section taken along the line '8--8 of Fig. 7; Figs. 9 and 10 show amodication of the arrangement shown in Figs. I and 8, Fig. 9 showing the right half in plan and the left half in section along the line 9 in Fig. 10, and Fig. 10 being an elevation of the left half ot Fig. 9 with the right half in section taken along the line IU-Ill in Fig. 9; Figs. 11 and 12 show a further modification of the form of the invention illustrated in Figs. 4 to 6, Fig. 11 showing the right half in plan and the left half in section along the line II-II in Fig. 12, and Fig. 12 showing the left half of Fig. 11 in elevation and the right half in section taken along the line I2--I2 in Fig. 11; Figs. 13 and 14 show a modification of the arrangement shown in Figs. l1 and 12, Fig. 13 showing the right half in plan and the left half in section along the line i3 in Fig. 14, and Fig. 14 showing the left half of Fig. 13 in elevation and the right half in section i of a piston. The edges of the plate I may be supported in any desired manner, for example, in the housing formed by a ring 5 and a cupshaped housing member 6 clamped together by bolts 1, a watertight gasket 8 being interposed between the plate and the housing. The plate' thus closes the open end of the housing.

In the interior of the housing upon the back of the thicker portion of the plate I there are mounted one or more elongated members 9. These, if more than one. `are arranged parallel to each other and may be held to the plate I by means of the screws I0. If desired. the members 9 may be integral with the member l. On the sides of the members 9 and integral therewith there are formed laterally extending ribs Il which act as vibratory reeds. Upon the upper surfaces of the reeds II there are mounted one or more piezoelectric crystals I2 preferably of Rochelle salt. The crystals I2 must be firmly secured to the surface of the reeds in any suitable manner, for example, by cementing, for. as will presently appear, the forces generated between the crystals and the members II are in shear. If the members Il are of metal as shown, they will serve as one electrode for the crystals. The second electrode I3 is secured to the top of each crystal in any suitable well-known manner. Should the members 9 and II be made of other than electrically conducting material. it will be necessary, of course. to provide a second electrode between` the crystal and th'e member II as will be understood by those skilled in the art.

The upper electrodes I3 are shown connected by strips of foil I 4 or other suitable conductors to a bus bar I5 which is secured to an insulating strip I6 by means of right-angle tabs I'l and rivets I8. The insulating strip I6 is in turn supported by insulating spacers I9 and screws 20 upon the top of the several members 9. Connected in this way al1 the crystals on each element 9 are connected in parallel with each other. The several groups of crystals so formed may th'en also be connected in parallel as shown or they may be connected in series or in series parallel, depending upon the electrical conditions existing. The elements 9, being connected together through the member I and the screws lli. are grounded to the case of the instrument by the leads 2| and 22.

Active and ground conductors 23 and 24 may pass out oi. the case through the watertight stufng tube 25.

The device may be used both to transmit and to receive compressional waves under water or other liquid medium. For transmitting, an electroinotlve force is applied between the conductors 23 and 24 and thereforev across two opposite faces of the crystals I2. These are out in such a manner that upon the application of an alternating electromotive force to the electrodes, the crystals will elongate and contract in the direction of their the crystals of a sinusoidal alternating potential results in a bending vibration of the 4reeds II. This is transformed into a vertical vibration of the members 9, as seen ln Fig. 2, of a frequency determined by the frequency ofthe exciting alternating potential. This preferably is made to coincide with the natural frequency of the reeds Il. 'I'he vibration of the members 9 is transmitted to the surface 2 of the plate I whence it is radiated into the surrounding medium.

The oscillator so Aformed is highly efficient and has a very low internal damping. Moreover, by properly proportioning the masses of the vibrating reeds and the members 9 and I, a suitable amplitude transformation can be obtained between the reeds and radiating surface 2 for eilicient radiation into a liquid medium.

When the device is used for receiving signals.'

the action is reversed. Compressional wave vi-f';

brations in the medium vibrate the plate I andl the members 9, which in turn produceexural vibrations of the reeds II. This sets up elongation and contraction of the crystals, resulting in the appearance of an alternating force across the crystal faces.

If desired. the members 9 may be cut between adjacent crysta1s,`as, for example. along the lines 28 and 21 in Fig. 1 so that each crystal section is isolated. The several crystals may then be excited with different voltages resulting in nonuniform amplitude distribution whereby any desired beam patternv in the medium can be obtained.

Fig. 3 shows a mid-sectional'view of a fragment anale? members 32 and 33, upon the plate I between the ribs 28 as shown in Fig. 5. The ribs 28.may be cut transversely as at 34 and 35 in Fig. 6 between separate crystals so that the various crystals may be excited with different voltages for the production of non-uniform vibrating amplitudes at the radiating surface 2 whereby any desired beam pattern can be obtained. The specific beam pattern is controlled by the form of vibration of the radiating elements in a manner which is generally treated .in the British Patent No. 279,878 by giving a large diaphragm a somewhat greater amplitude at the center than at the edges and maintaining the amplitude over the whole diaphragmin the same phase. In this manner it is possible to create a sound intensity pattern of radiation which will have a large intensity loop normal to the radiating surfaces and very small secondary effects at inclined angles to the normal.

The unit may be supported in a housing 6 closed on one side by the plate Iwhich is held in position bythe ring 5 and the bolts 'I as in the preceding modiiication. The interior of the housing is filled with air or other gas. Thus the vibrating elements 28 have one end free and the other end loaded by the mass I and the signaling medium, whereby any desired amplitude transformation can be obtained. This structure has par ticular merit in the simplicity of its construction since the elements 28 and plate I can easily be formed from a single block of material by simple millingjoperations.

n The action of the piezoleetriof crystals in this modification is similar to the preceding one, that is the forces of vibration are transmitted between the crystals and the ribs 28 in shear, although there is, oi

course, no bending action, all the crystals being of a modification of the arrangement just described. In this modification crystals are placed on both top and bottom of the reeds l I. The crystals on the bottom must be cutalong the opposite axis from those on the top so thatwhen all the crystals are excited'in phase, the top crystals will expand whilethe bottom crystals contract, and vice versa. The power output of the device both as transmitter and receiver can thereby be increased considerably.

The vibrating systemcomprising reeds formed on half wave length members is also operable by electromagnetic means as shown and claimed in my copending application, Serial No. 333,157 filed May 3, 1940.

In the modification shown in Figs. 4 to 6 the vibrating reeds are not used, but elongated ribs 28 are formed integral with the plate I. These ribs have a, height of approximately onefquarter of a wave length to form with the thickened portion of the plate I a one-half wave length vibratenergized to expand simultaneously and to contract simultaneously.

Both of the modifications Just described provide I an electroacoustic transducer having a substantially plane piston-radiating surface. As is well known in the art if the dimensions of the radiating surfaceare made large compared with the wave length of compressional waves in the signaling medium, the device will have a beam pattern in which most of the energy transmitted and the sensitivity pattern for reception will have an energy concentration in the direction of the axis perpendicular to the radiating surface. In some cases it may be desirable to be able'to radiate and receive large amounts of energy in all directions especially in all direction in a plane. For this purpose a radiating surface which is cylindrical and which vibrates radially is desirable.

Figs. 7 and 8 show a modification of my in.. vention which provides such a cylindrical radiating surface. In these figures the radiating element 4| having a cylindrical radiating surface 42 and provided at its ends with a nodal flange 83 hasl mounted on its inner face a plurality of elongated vibrating elements M all mounted with their long dimensions parallel to the axis of the cylinder and projecting radially from the internal surface of the member M. The elements M are secured to the element 4| by means of screws ,Ml which are sunk into the outer face of the element BI, the resulting holes being made watertight by the plugs 46. 'I'he members M are similar to the members 9 in the modifications `previously described with reference to Figs. l to 3. The members M have formed along their sides near their inner ends vibratory reeds 41. Upon the surfaces of'the reeds 41 there are mounted one or more piezoelectric crystals 88 preferably ci Rochelle salt. 'Ihe crystals 8 are mounted on the reed. as previously described, with their vibrational axes parallel to the surface of the reeds so that the transfer of vibrations between the crystals and the reeds takes place with the aid of shearing forces. -As in the previous modification the reeds themselves may serve as one electrode for the crystals while the second electrode may be secured to the topof the crystal and connected to bus bars 49 mounted on the members yM. The several sets of crystals may be connected in any desired series and/or parallel arrangements for example, for parallel connection the several bus bars 4.9 may be connected to a ring 55.

The two ends of the cylindrical structure may be closed by cover plates v5|l and 5| which may be held by means of screws 5H against anges b2 and 53 formed at the ends of the radiating member di. The ring 55 may then be supported on the cover 5l and leads therefrom may be taken out through a watertight gland 56. If desired, the outer radiating surface of the element ytill may be `cut axially as at 51 to reduce.

the radial stiffness of the member 4I.y Moreover the elements M may be sectioned diametrilcally into a plurality of elements, correspond-v ing circumferential cuts being made on the outer surface of the element 4i as shown at 58. The operation of the device is substantially the same as that described with reference to Figs. 1 to 3.

For transmitting, an electromotive force applied across opposite faces of the crystals causes the same to elongate and contract in directions substantially perpendicular to the radial axes of the members M of which the reeds 51 form a part, for example, as indicated for one element tl by the arrows 59. The forces tending to expand the crystals are transmitted by shearing action to the reeds 41 resulting in a exural vibration oi' the reeds. This is transformed to a radial vibration of the members 4t and radiating member M. determined by' the frequency of the exciting alternating potential which `is preferably made to coincide with the natural frequency of flexural vibration of the reeds $1. Moreover the elements M together with the respective portions of the radiating member t I which effectively vibrate therewith are preferably adjusted in length and weight so that they form a one-half Wave length vibrational system in the radial direction at the natural frequency of vibration of the reeds H. Compressional waves are thereby radiated from the entire external surface of the cylinder in all directions. If the height of the cylinder be made large compared with the wave length of compressional waves in the signaling medium at the signaling frequency, the radiation will be con `centrated in a plane perpendicular to the axis oi the unit.

The further modification of my invention which isshown in Figs. 9 and 10 is the reverse of that shown in Figs. 7 and 8 in that the radiation ci compressione] wave energy is directed toward the central axis of the unit where it may be applied to the treatment of liquids or other substances. Here the-internal cylinder 6| having a radiating surface 62 has mounted on its external surface a plurality of vibrating elements tt by means of the screws 65 which may be made watertight by the lead washers 10. As in the one electrode formed by one of the members 64 and its other electrode connected to one o1' the bus bars B9. The operation oi this device is substantially the same as that just described 'with reference to Figs. 7 and 8 except that the radial vibrations of the radiating surface B2 are directed toward the axis of the cylinder. For the treatment oiI liquids with compressional waves the end of the cylinder may be closed by means of cover plates 1I and 12 secured by screws 13 to anges 14 and 15 formed at the ends of the radiating element Bl just beyond the nodal supporting webs 63 through apertures at the center of plates 1| and 12. A pipe 16 may be provided for conducting liquids to be 'treated along the axis of the cylinder. The interior of the device surrounding the pipe 16 may be completely filled -with oil or other compressional waveconducting liquid by means of the iilling plug 11.

Figs. 11 and l2 show another modification of my invention providing a cylindrical radiating vibrating surface capable of transmitting compressional waves outwardly in substantially all A directions and of receiving from substantially all The frequency of vibration is preceding modification, the elements B4 are provided with ilexurally vibratable reeds 61 on which are mounted piezoelectric crystals I88, each having directions. The radiating surface 82 of the radieting member 8l is operated by elongated riblike members 88 which are similar to the members 28 in the modifications shown in Figs. 4 to 6. The members B8, however, are elongated in the axial direction and extend radially .from the member 8| to formtherewith a plurality of onehalf Wave length vibrating elements. These have secured to their sides a plurality of piezoelectric crystals 89 one of whose electrodes is formed by the members 88 and the other being connected to bus bars 83 which .may be mounted on the member 8| between the elements 88. For parallel connection of the crystals the bus bars 88 may all be connected to a ring 84 positioned at one end of the structure. The radiating surface of the element 8| may be cut axially as at 85 to reduce the stillness of this member to radial vibration, Further, the members 88 may be sectioned diametrically as indicated, for example, at 8B in Fig. l2. Corresponding circumferential cuts may also be made in the radiating surface in the element 8| as indicated at 81. The interior of the unit may be made watertight by .cover plates 9U and 9| secured to flanges on the mernber 8| as shown. The operation of this modification is substantially the same as that described with reference to Figs. 4 to 6. The vibrational axes oi the crystals are oriented to produce expension and contraction of the crystals in the direction parallell to the sides of the members 88 upon which theyA are mounted as indicated,

for example, by the arrow 92, in Fig. l1 and the.

arrow 93 in Fig. 12. The vibration of the crystals is transmitted by yshearing forces to the members 88 causing them and the member 8| to vibrate radially. In receiving compressional waves the action is, of course, reversed, the radial vibration of the memberl and the members 88 being transferred to the crystals which produce corresponding electromotive forces.

The modication of my invention shown in Figs. 13 and 14 is similar to that shown in Figs. 1l and 14 with the exception that the radiation is fdirected inward toward the axis of the cylinder. The cylindrical member I0| having radiating surface |02 has'mounted on its external surface a plurality of rib-like members |08, preferably forming with the radiating member ||J| a. plurality ci one-half wave length radially vibratory elements. On the sides of members |08 uid-conducting pipe may to Figs. 11 and 12 except that a shear movement of members |08 form one electrode for the crystals,

the other electrodes being connected to bus bars |03 mounted on the member |0| between the members |09. For parallel operation of the crystals the several bus bars may conveniently be connected to a collector ring |04 mounted on a flange |05 formed on the member |0|. The interior of the structure may be closed by cover plates |06 and |01 fastened to theflanges |05 and I formed on the radiating member. -A liqbe'passed through central apertures in the cover plates |06 and |01, the joints being made liquid tight rwith suitable packing material. The interior of the unit may befilled with oil or other compressional waveconducting liquid through ,the -iillingplug H2.

' `The operation of this modification is substantially the same as that described with reference the radial vibrations of the radiating member are directed inwards toward the axis of the cylinder whereby liquids conducted through the pipe can be subjected to intense compressional wave vibrations.

Having now described my invention, I claim:

1. In an electroacoustic device, in combination, a piezoelectric operating means comprising piezoelectric crystal elements, means mounting said crystal elements to operate the same by a shear movement including a longitudinally vibrating element having a free end with said crystal-mounting means projecting substantially at right angles therefrom and vibrating transversely to its length near the free end, and a radiating member on which said longitudinally vibrating element is mounted substantially normally thereto. i

2. In an electroacoustic device, in 'combination, a piezoelectric operating means comprising piezoelectric crystal elements, mounting means having a high modulus of elasticity and means cementing said crystal elements to the surface of said mounting means, said crystal elements having their electrodesv in planes substantially parailel'to the mounting surface of said mounting means whereby said crystals may be operated by said mounting means, a longitudinally vibrating element having a free end from the vicinity of which said mounting means projects laterally, and a radiating member on which said crystal-vibrating element is mounted substantially normally thereto.

3. In an electroacoustic device, in combination, a, vibratory mounting unit lcomprising a longitudinally vibrating element having a free end, a mounting reed projecting laterally from the longitudinally vibrating element near its free end, said reed having a nat surface parallel to v trodes extending parallelly to its length dimension, piezoelectric crystal elements, means cementing saidpiezoelectric crystal elements on the mounting surface of said reeds, said piezoelectric crystal elements having elecsaid mounting surwhich said faces, and a radiating member on longitudinally vibrating element is mounted substantially normally thereto.

4. In an electroacoustic device, in combination, a vibratory mounting unit comprising a 1ongitudinally vibrating element having a free end, amounting reed projecting laterally from the longltudinallyvibrating element near its free end, said reed having a flat surface parallel to its length dimension, piezoelectric crystal elements, means cementing said piezoelectric crystal elements onthe mounting surface of said reeds, said piezoelectric crystal elements having electrodes extending parallelly to said mounting surfaces, and a. radiating member on which said longitudinallyvibrating element is mounted substantially normally thereto, said longitudinally vibrating element'being tuned for the frequency it is desired to have the electroacoustic device operate.

5. In an electroacoustic device, in combination, a vibratory mounting unit comprising a longitudinally vibrating element having a free end, a mounting reedprojecting laterally from the longitudinally vibrating element near its free end,

said'reedhaving a flat surface parallel to its length dimension,.piezoelectric crystal elements, means cementing said piezoelectric crystal elements on the mounting surface of said reeds, said piezoelectric crystal element-s having electrodes extending parallelly to said mounting surfaces, and a radiating member on which said longitudinally vibrating element is mounted substantially normally thereto,said vibrating reed and said l l l longitudinally vibrating element being tuned Substantially for the desired frequency at which said The following references are of record in the file of this patent:

I:nrs PATENTS UNITED sr Number Name Date 1,803,274 Sawyer Apr. 28, 1931 Re. 20,213 Sawyer Dec, 22, 1936 2,190,666 Kollmeyer Feb. 20, 1940 1,097,859 Hecht May 26, 1914 2,163,649 Weaver June 27, 1939 2,163,650 Weaver June 27, 1939 FOREIGN PATENTS Number Country Date 279,878 British Mar. 8, 1928 301,034 British Feb. 21, 1930 511,307 German Oct. 29, 1930 

